Electronic flash device

ABSTRACT

Electronic flash apparatus for photographic purposes, comprising a flash tube and a series of capacitors providing power for flashing the flash tube. When the flash tube is triggered, only one capacitor is connected across the flash tube. One or more additional capacitors are then switched into the flash tube circuit, for additional flash illumination, depending upon the amount of light required for the photograph. In one embodiment of the invention, the switching of additional capacitors into the flash tube circuit is controlled by the amount of light reflected from the subject being photographed.

United States Patent 1191 1 1 3,725,734 Schneider 1 1 Apr. 3, 1973 s41ELECTRONIC FLASH DEVICE 3,515,938 6/1970 Morse ..315 241 R x Inventor:Arthur schneidgr wiesenweg, 3,546,529 12/1970 Griffin ..3l5/24l P yFOREIGN PATENTS OR APPLICATIONS 1 1 AssigneeI Rolli-werke Franks &Heidecke, 839,768 6/1960 Great Britain ..315/241 P Braunschweig, Germany[22] Filed: Man 9 1971 7 Primary Examiner-Roy Lake Assistant Examinerl,awrence J. Dahl PP N03 122,411 Attorney-Charles Shepard and Stonebraker&

Shepard [30] Foreign Application Priority Data ABSTRACT Mar. 11, 1970Germany ..P 20 11 432.3 Mar. 13, 1970 Germany ..P 20 11 905.5 P, gPhotograph? purpisesi comprlsmg a as tu e an a serles o capacitors Mar.14, 1970 Germany ..P 20 12 150.0 providing power for flashing the flashtube" when the flash tube is triggered, only one capacitor is connected[52] US. Cl. ..3l5/241 P, 315/151, 331155//l25496 across the flash tube.one or more additional p {51] Int Cl Hosb 37/00 tors are then switchedinto the flash tube circuit, for [58] Field of Search... ..315/151 159227 241 R 241 addmmal flash dependmg the P amount of light required forthe photograph. In one embodiment of the invention, the switching ofaddi- [56] References Cited tional capacitors into the flash tubecircuit is controlled by the amount of light reflected from the sub-UNITED STATES PATENTS i being Photographed- 3,590,314 6/1971 Krusche..315/ 159 10 Claims, 5 Drawing Figures PATENTEDAFR3 ms 3.725734 SHEET 10F 3 3 25 26 i 21 22 1 m m 5 6 1O 7 9 a E I Fig. 1

PATENTEDAPM I973 ST 6 0 aT wT 1 1 m 3 z W ,1: 2

ELECTRONIC FLASH DEVICE The subject invention applies for electronicphotographic flash devices having several parallel-to-theirflash-tubeoperable or switchable storage capacitors.

With such units the capacitors are circuited directly in parallel withthe flash tube, so that on this being triggered, they discharge jointlyover it. To adapt the resultant power consumption to actual incurredrequirements, the necessary total capacity was provided for by a manualonor off-circuiting respectively of several individual capacitors. Withthe total power available not called for, a certain number of additionalcapacitors must be switched off and, provided an effective saving inpower is to be achieved, the necessary rating must be accuratelyestimated prior to every individual exposure.

The purpose of the subject invention is to self-determine the requiredpower rating in such a manner that the first capacitor remains alwayscircuited in parallel with the flash tube. The remaining ones are, viaelec tronic switches (switching diodes, thyristors, SCR), interlinkedwith the flash tube and are, by means of a photoelectric measuringdevice connected, in the required number, parallel to the flash tube.

This can be achieved by various means. For one, it can be so effectedthat subsequent to the triggering of the flash tube and the commencementof main capacitors discharging, the auxiliary capacitors are stepwiseconnected up and that this switch-on procedure is interrupted once theluminous intensity measured by the photoelectric measuring device hasreached the preselected value, i.e., the photograph to be taken iscorrectly exposed.

Provided the flash unit is furnished with a photoelectrically controlledquenching device, i.e., a quench tube or thyristor which, on obtainmentof the pre-set luminous intensity, short-circuits the flash tube, thequench tube current can be used to avert or interrupt respectively thedischarging of the not yet switched-on or not yet discharged additionalcapacitors respectively. This can also be accomplished by aphotoelectric measuring device which, on reaching the pre-setthreshold-value of the luminous intensity, generates an impulse which,in turn, interrupts a further on-circuiting of the auxiliary capacitors.Lastly, there can be provided in lieu of an integrating measuringphotoelectric device, a photodiode or a photothyristor (LASCR) which,after a defined period subsequent to the flash tubes ignition, generatesa voltage impulse proportional to the measured reflexion light intensityand which then determines the number of auxiliary capacitors to beactivated and those not.

The appended drawings show several design examples.

FIG. 1 depicts a circuitwith automatic, sequential or successiveon-circuiting of auxiliary capacitors with resultant interruption ofthis on-circuiting sequence by the quenching tube.

FIG. 1A illustrates a modification of the right hand portion of FIG. 1,substituting a quenching thyristor for the quench tube.

FIG. 2 shows a similar lay-out where, however, the interruption of theon-circuit function is effected by an additional impulse generated by aseparate photoelectric measuring device.

FIG. 3 displays a combination of the afore-mentioned design lay-outs,utilizing a photodiode and, finally,

FIG. 4 shows a circuit design in which a nonor a short-time integratingmeasurement is carried out and where, subsequent to the triggering ofthe main flash tube, there are circuited-on the necessary number ofauxiliary capacitors at once.

Flash tube 1 is depicted with the conventional type ignition electrode2, the actual ignition circuit being no different from the generallyknown arrangements. The triggered or ignited flash tube 1 can bequenched prematurely by short-shunting. As a shunting means there is,for instance, used a SCR- or a quenching tube 3. The photoelectricmeasuring device generates a voltage proportional to the luminousintensity which, on exceeding an ajustable preselected threshold value,supplies the triggering or ignition impulse for the quenching tube 3.

Measuring devices of this type are known, for which reason no detailedexplanation may be given. However, it is deemed worth mentioning thatthe subject invention is not necessarily or positively dependenton anintegrating measurement of the light or intensity, there can be utilizedalso a short-time or punctiform measurement of the light reflected bythe object being photographed this being explained in detail further onin this paper under the design lay-out as per FIG. 4.

In our design example, the feed capacitors overall capacity issubdivided among three capacitors viz. 5, 6 and 7 which, via the feedcable 8, are charged over diodes 9, l0 and 11. Capacitor 5 is, via diodel2, interconnected with flash tube 1 and capacitors 6 and 7 overswitching diode or thyristors (SCR) l3 and 14. On ignition of flash tube1, there initially discharges capacitor 5 via the flash tube. In thiscase, there ensues a voltage drop on the thyristors or switching diodesl3 and 14 respectively, leading to the charging of capacitors 15 and 17via their counterparts 16 or 18, respectively. The series resistance ofcapacitor assembly 17, 18 and of resistance 20 is greater than that ofcounterpart capacitors 15, 16 and resistance 19, so that the chargingperiod of capacitors varies. The trigger diodes 21 and 22 areintercircuited between these potential dividers l5, 16, or 17, and 18respectively and thyristors 13 and 14. Thyristors 25 and 26 are arrangedin parallel with capacitors l5 and 17. Incorporated in the circuit ofthyristors 25 and 26 are resistors 27 and 28, the latter are connectedin series in the discharge circuit of quench tube 3. Rating ofpotentiometers 15, 16, 19 or 17, 18 and 20 respectively is such thatfollowing the flash tube 1 ignition and towards end of discharge ofinitial capacitor 5, there is obtained the switching voltage on triggerdiode 21, leading to a triggering of thyristor 13, this in turninitiating discharge of capacitor 6. Towards the end of capacitor 6discharge, trigger diode 22 activates thyristor 14, thus initiating adischarge of capacitor 7.

If during discharging of capacitor 5 achieving of the preselected valueof the luminous intensity, a photoelectric-monitored ignition of tube 3becomes effective, then discharge current of tube 3 will initiate avoltage drop at resistors 27 and 28, leading to a triggering ofthyristors 25 and 26 and thus shorting the capacitors 15 and 17,rendering action of trigger diodes 21 and 22 ineffective. Providedtherefore the photo flash action is interrupted on attaining therequired luminous intensity due to triggering of tube 3 or thyristor 3the residual energy of flash capacitor 5 is nullified, however,discharge of remaining capacitors 6 and 7 is prevented. With thelight-monitored interruption of flash discharge, with capacitor 6already spent, on-circuiting of third capacitor 7 is averted. Diode 12prevents the wasteful re-charging of the discharged capacitor 5 duringthe subsequent ensuing discharge of counterparts 6 and 7.

That afore-said applies likewise for thyristors 13 and 14. Duringrecharging process, parallel resistors 23 and 24 prevent a reloading ofcapacitors and 17.

The current flow through tube 3 during ignition process is very high sothat for the generation of the required control of voltages forthyristors 25 and 26 only low-rated resistors 27 and 28 are needed togenerate the necessary voltage drop; their influence on the resistanceof quenching circuit 3 therefore is small,

The layout example shows a distribution of the storage capacity overthree capacitors 5, 6 and,7. It goes without saying that a subdivisioninto an arbitrary greater number of partial capacitances is possible.

As the energy requirements or ratings of a photographic flash unitincreases with the square of the subject distance, there is recommendeda quadratic or exponential stepping of capacitance values. With asixstep division there might consequently be obtained the followingcapacity series:

and a total capacity of 480 .pF would be composed of the followingcapacities In the case of a unit having a guide member of 18 this wouldalready correspond to a i A lens stop.

With the design layout as per FIG. 2 we have basically the same build-upas that shown in FIG. 1. The difference is that the thyristors 25 and 26are not triggered by resistors 27 and 28 voltage drop action, namely atthe moment of ignition of quenching tube 3 but that the control of thethyristors or switching diodes 25 and 26, via connecting cable 4a, waseffected directly by a photoelectric measuring device, irrespectivewhether this simultaneously also ignites quenching tube 3, overelectrodes 4 or whether for this quenching tube a special and additionalphotoelectric measuring device, as the generally known type, isprovided.

FIG. 3 displays a further design variation which differs as regards theluminosity measuring layout. In all other respects the build-up isidentical to that of FIG. 2 for which reason there were also utilizedthe same reference types for identical components.

Phototransistor 31 is connected to trigger diode 21. On ignition offlash tube 1, i.e., on discharge of capacitor 5, on the thyristors 13and 14 a voltage drop occurs so that on attainment of breakthroughvoltage, trigger diodes 21 and 22 are through-circuited. Contemporarilyphoto transistor 31 is supplied with drop voltage until on attainment ofthe breakthrough voltage of trigger diode 21, the voltage breaks down.The measurement is therefore carried out within a fixed and pre-setperiod of time. In case of exceptionally intensive brightness triggeringvoltage of thyristors 25 and 26 is reached earlier than breakthroughvoltage of trigger diode 21. This shunts capacitors 15 and 17,preventing a further voltage increase on trigger diodes 21 and 22. Withlesser brightness, trigger voltage of thyristor 25 occurs later thantrigger diodes 21 breakthrough voltage. Ac-

tion of resistors 32a and 33a permits a setting of the desiredon-circuit. The comparatively low-rated resistors 27 and 28 should, whenutilizing a quench tube 3, generate a voltage drop which triggersthyristors 25 and 26 thus averting renewed voltage increase on triggerdiodes 9 and 10, on quench tube 3 being triggered.

FIG. 4 shows a further modification. I-Iere, measurement andoncircuiting of all needed auxiliary capacitors takes place immediatelyfollowing the triggering of the flash tube by a measurement of thebrightness of luminous intensity. The resultant action generates animpulse the voltage amplitude of which is proportional to the measuredbrightness.

This voltage amplitude then determines the number of auxiliarycapacitors to be switched on or off, respectively. Basic layout isidentical to that described prior. In parallel with the main capacitoror a flash tube circuit, there is ranged a capacitor-294 for the energysupply of photo transistor 31.

The photo transistor measures, during a short interval determined by thecharging of capacitor 29a, the brightness reflected by the subject beingphotographed. This time interval is essentially shorter than that whichmust expire until capacitors 15 and 17 have attained the switchingvoltage of trigger diodes 21 and 22 and until the thyristors l3 and 14trigger, thus initiating the discharge of capacitors 6 and 7 via thetube 1. The subject reflection light impinging on photo transistor 31generates a voltage amplitude in induction 32, the height of whichcorresponds to the reflected luminosity. This voltage amplitude triggersthyristors 25 and 26 to the extent that their trigger voltage isexceeded. During the above, capacitors 15 and 17 are short-circuited sothat trigger diodes 21 and 22 switching voltage is not reached andtherefore the through-circuiting of transistors 13 and 14 or dischargeof capacitors 6 and 7 fails to take place.

It will be noted from the design example that induction coil 30a isprovided with tappings 33, 34, 35 and 36 which are interlinked with theindividual transistors 25 and 26 etc. On the voltage amplitude of thesetappings exceeding the switching voltages of thyristors 25, 26 etc. noon-circuiting of the auxiliary capacitors will take place.

If voltage amplitudes exceed only partially the switching voltage ofthyristors 25 and 26, only such capacitors 6, '7 will be on-circuitingwhere or during which thyristors 25 and 26 were not through-circuited.Note from the drawing that a random number of auxiliary capacitors canbe catered for. In lieu of the depicted inductive tapping, the varyingresponse sensivity of the thyristors 25 and 26 can also be achieved bycorresponding voltage dividers in which case all thyristors 25, 26 etc.are connected to a common voltage amplitude of induction 32.

Considered chronologically there takes place immediately following theignition of flash-tube l, the measuring of the luminous intensity by aphoto transistor 31, and there is generated a voltage amplitude theintensity of which finds or determines the extent of switching-off ofcapacitors 15, 17. Immediately following this, there are triggered thethyristors 13, 14 etc, of the non-switched off capacitors and thedischarging those capacitors 6, 7, etc. is initiated. Triggering ofthyristors 25, 26 etc. takes place simultaneously as does also thetriggering of the thyristors 13, and 14 provided that no deviatingcomponent ratings, specifically the capacitance of capacitors 15, 17,are to effect a stepwise sequence or provided such sequence is desired.

In the case of the described subject lay-out the oncircuiting ofauxiliary capacitors is effected by the short-circuiting or shunting ofcapacitors 15 and 17, the latter triggering for the power needs ofdiodes 21 and 22 and which, on attaining breakthrough voltage, triggerthyristors 13 and 14. Needless to say here that there can be provided inlieu of this short-circuit arrangement for capacitors 15 and 17 also apositive style cut-in control of such design that instead of adisconnection of triggered diodes 21 and 22 or the operating capacitors15 and 17 of these, there is effected an oncircuiting.

What I claim is:

1. Electronic flash apparatus for photographic purposes, comprisingflash tube means, a series of individual capacitors for powering saidflash tube means, said series of capacitors being connected in parallelwith each other and with said flash tube means, each capacitor exceptthe first one of said series having electronic switch means shiftablebetween a non-conducting state and a conducting state and effective,when in a non-conducting state, to prevent discharge of its associatedcapacitor through said flash tube means, means for charging all of saidcapacitors and placing all of said electronic switch means in anon-conducting state, in preparation for a flash, and control meansresponsive to discharge of one capacitor in the series for shifting theelectronic switch means of the next succeeding capacitor of the seriesto its conductive state so that such next succeeding capacitor may thendischarge.

2. Apparatus as defined in claim 1, wherein said flash tube meanscomprises a single flash tube through which said individual capacitorsdischarge in succession.

3. Apparatus as defined in claim 1, wherein said electronic switch meanscomprises a separate thyristor operatively interposed in the dischargecircuit of its associated capacitor.

4. Apparatus as defined in claim 3, wherein each of said thyristors (13or 14) has a gate circuit operatively connected to a trigger diode (21or 22).

5. Apparatus as defined in claim 4, wherein each of said trigger diodes(21 or 22) is part of a control circuit including auxiliary capacitors(15, 16 or 17, 18) and a second thyristor (25 or 26) operativelyconnected to one terminal of said flash tube means (1).

6. Apparatus as defined in claim 1, further comprising light integratingmeans for terminating duration of a flash produced by successivedischarge of said series of capacitors through said flash tube means.

7. Apparatus as defined in claim 4, further comprising a phototransistor (31) operatively connected to said triggler diodes (21, 22)and effective, in response to a pre etermmed threshold value oflightreceived thereby, to prevent discharge of additional capacitors ofsaid series of capacitors.

8. Apparatus as defined in claim 1, further comprising an induction coil(30a, 32) having a plurality of taps (33, 34) each operatively connectedto the control means (13, 21, 25, etc. or 14, 22, 26, etc.) forcontrolling discharge of one of the capacitors, respectively, of saidseries of capacitors, and a photo transistor (31) operatively connectedto said induction coil and effective, when a predetermined thresholdvalue of light is received by said photo transistor, to generate avoltage in said coil sufficient to operate said control means to avoiddischarge of further capacitors of said series.

9. Electronic flash apparatus for photographic purposes comprising aflash tube (1), a first capacitor (5) in parallel with said flash tubeand arranged, upon initiation of a flash, to be discharged through saidflash tube, a second capacitor (6) operatively connected to said flashtube through first electronic switch means (13) which is normallynon-conductive, first switch control means responsive to flow of currentfrom said first capacitor through said flash tube for rendering saidfirst electronic switch means conductive so that said second capacitormay then discharge through said flash tube, a third capacitor (7)operatively connected to said flash tube through second electronicswitch means (14) which is normally non-conductive, and second .switchcontrol means responsive to flow of current from said second capacitorthrough said flash tube for rendering said second electronic switchmeans conductive so that said third capacitor may then discharge throughsaid flash tube.

10. Apparatus as defined in claim 9, further comprising means responsiveto light reflected from a subject to be photographed, for terminating aflash in said flash tube when the quantity of said reflected lightreaches a predetermined threshold value.

UNIT ED STATES PATENT OFFICE CER-TIFICATE OF CORRECTION Patent No.3,725,734 0 Dated April 3, 1973 Invent0 Arthur Schneider It is certifiedthat error appears in the above-identified patent and that said LettersPatent are hereby corrected as shown below:

On the cover sheet [75] "Wiesenweg, Germany" should read Voelkenrode,Germany Signed and sealed this 28th day of August 1973.

' (SEAL) Attest:

EDWARD M.FLETCHEIR,JRI. RENE D.,TEGTMEIYER v 1 Attesting Officer ActingCommissioner of Patents 7 FORM po'mso USCOMM-DC sous-P69 I i ".5.GOVIINMI!" PRINTING OFFICE II. O-JGC-334.

1. Electronic flash apparatus for photographic purposes, comprisingflash tube means, a series of individual capacitors for powering saidflash tube means, said series of capacitors being connected in parallelwith each other and with said flash tube means, each capacitor exceptthe first one of said series having electronic switch means shiftablebetween a non-conducting state and a conducting state and effective,when in a nonconducting state, to prevent discharge of its associatedcapacitor through said flash tube means, means for charging all of saidcapacitors and placing all of said electronic switch means in anon-conducting state, in preparation for a flash, and control meansresponsive to discharge of one capacitor in the series for shifting theelectronic switch means of the next succeeding capacitor of the seriesto its conductive state so that such next succeeding capacitor may thendischarge.
 2. Apparatus as defined in claim 1, wherein said flash tubemeans comprises a single flash tube through which said individualcapacitors discharge in succession.
 3. Apparatus as defined in claim 1,wherein said electronic switch means comprises a separate thyristoroperatively interposed in the discharge circuit of its associatedcapacitor.
 4. Apparatus as defined in claim 3, wherein each of saidthyristors (13 or 14) has a gate circuit operatively connected to atrigger diode (21 or 22).
 5. Apparatus as defined in claim 4, whereineach of said trigger diodes (21 or 22) is part of a control circuitincluding auxiliary capacitors (15, 16 or 17, 18) and a second thyristor(25 or 26) operatively connected to one terminal of said flash tubemeans (1).
 6. Apparatus as defined in claim 1, further comprising lightintegrating means for terminating duration of a flash produced bysuccessive discharge of said series of capacitors through said flashtube means.
 7. Apparatus as defined in claim 4, further comprising aphoto transistor (31) operatively connected to said trigger diodes (21,22) and effective, in response to a predetermined threshold value oflight received thereby, to prevent discharge of additional capacitors ofsaid series of capacitors.
 8. Apparatus as defined in claim 1, furthercomprising an induction coil (30a, 32) having a plurality of taps (33,34) each operatively connected to the control means (13, 21, 25, etc. or14, 22, 26, etc.) for controlling discharge of one of the capacitors,respectively, of said series of capacitors, and a photo transistor (31)operatively connected to said induction coil and effective, when apredetermined threshold value of light is received by said phototransistor, to generate a voltage in said coil sufficient to operatesaid control means to avoid discharge of further capacitors of saidseries.
 9. Electronic flash apparatus for photographic purposescomprising a flash tube (1), a first capacitor (5) in parallel with saidflash tube and arranged, upon initiation of a flash, to be dischargedthrough said flash tube, a second capacitor (6) operatively connected tosaid flash tube through first electronic switch means (13) which isnormally non-conductive, first switch control means responsive to flowof current from said first capacitor through said flash tube forrendering said first electronic switch means conductive so that saidsecond capacitor may then discharge through said flash tube, a thirdcapacitor (7) operatively connected to said flash tube through secondelectronic switch means (14) which is normally non-conductive, andsecond switch control means responsive to flow of current from saidsecond capacitor through said flash tube for rendering said secondelectronic switch means conductive so that said third capacitor may thendischarge through said flash tube.
 10. Apparatus as defined in claim 9,further comprising means responsive to light reflected from a subject tobe photographed, for terminating a flash in said flash tube when thequantity of said reflected light reaches a predetermined thresholdvalue.